1. Field
This application relates generally to wireless localization, and to localization between wireless devices.
2. Background
Various techniques are known for determining the location of an object. For example, a radar system determines the location of an object by directing radio frequency (“RF”) signals toward the object and detecting the signals that reflect off of the object. The distance of the object from the radar system may then be determined by analyzing the received signal to, for example, determine the time it takes for the signals to travel to the object and back.
Some tracking schemes employ a two-way ranging technique whereby each device involved in a distance determination operation employs a transceiver that sends signals to the other transceiver. For example, a first device that wishes to determine the relative distance to a second device may initiate a location determination operation by sending a signal to the second device. After receiving the signal, the second device sends a responsive signal back to the first device. The first device may then determine the distance between the devices based on the received signal. For example, the first device may determine the distance by calculating the time it takes for the signals to propagate between the devices.
Ranging techniques also may be employed to determine the relative direction between devices. For example, a tracking device may include multiple receive antennas, multiple transmit antennas, or both, that are spaced apart by a distance that is large enough to create sufficiently different signal paths for each antenna. The measuring device may then determine the relative direction to the device being tracked by triangulating signals received via each signal path. For example, a distance may be calculated between each antenna and the antenna of the device being tracked. The relative direction between the devices may then be determined based on these distances and based on the known distance between the antennas of the tracking device.
There are a number of situations where ranging techniques could potentially be used by a person to locate another object. For example, a person may wish to locate keys or another person (e.g., a child). In practice, however, a device that includes directional locating capabilities may be too large for certain applications due to the relatively wide spacing between the antennas. Moreover, such a device may utilize separate RF front-ends (e.g., transceivers) for each antenna, thereby increasing the cost of the device.